I. Field of the Invention
This invention relates to the combination of a current-limiting fuse and a loadbreak device for protecting an electrical apparatus such as a distribution transformer.
II. Description of the Prior Art
In the past various arrangements have been provided for utilizing protective fuses with transformers in order to protect the transformer from destruction by large fault currents. At one point in time the protective arrangement included a protective fuse link and a separate loadbreaking switch connected in series with a transformer winding. As the capacities of electrical distribution systems were increased, to deliver higher levels of power, increased power became available at a fault, and current-limiting fuses were provided for interrupting these large fault current. More recently the current limiting and loadbreaking functions have been combined in a single assembly such as disclosed in U.S. Pat. No. 3,628,092, issued Dec. 14, 1971. Further improvements on the Electrical Inductive Apparatus with Removable Protective Fuse, disclosed in U.S. Pat. No. 3,628,092, are claimed to be shown in U.S. Pat. No. 3,732,517 issued May 8, 1973 and in U.S. Pat. No. 3,792,215 issued Feb. 12, 1974. Both of the latter mentioned patents are directed toward improving the performance of the device with respect to interrupting the current and extinguishing the arc which develops upon interruption of the current. However, it has been found that there is still a need for further improvement in reliability of the current interrupting and arc extinguishing abilities of such combination current-limiting and loadbreaking devices. Further, it would be desirable to provide these improved performances with a simplified structure utilizing a minimum number of components.
Therefore, it is accordingly an object of this invention to provide a combination current-limiting and loadbreaking device which more reliably extinguishes the arc generated upon loadbreaking. Further, it is another object of the invention to provide the combined functions of current-limiting and loadbreaking with a mininum number of components in a device which is readily assembled but which still provides the desired improvement in operating performance.